Liquid crystal display (LCD) apparatuses have a lower power consumption and can be made smaller and thinner than cathode-ray-tube (CRT) apparatuses. Nowadays, various sizes of liquid crystal display apparatuses are widely used, ranging from small apparatuses such as mobile phones and digital cameras to large apparatuses such as large liquid crystal televisions.
Liquid crystal display apparatuses are classified into a transmissive type, a reflective type, and the like. Particularly, a transmissive liquid crystal display apparatus includes a liquid crystal display panel constituted by a pair of transparent substrates with a liquid crystal layer therebetween and a backlight unit serving as an illumination light source. Backlight units are classified into a direct-lighting type, in which a light source is provided directly under a liquid crystal display panel, and an edge-lighting type.
In general, a backlight unit for liquid crystal display apparatuses employs a condenser sheet, such as a prism sheet, a lens sheet, or the like, for orienting light emitted from a light source toward the front.
For example, a prism sheet includes a number of prisms each having a triangular cross section on a light-output surface thereof. The prism sheet condenses and orients light incident thereon toward the front by refracting and transmitting the incident light through inclined planes of the prisms. Particularly, for use in mobile apparatuses, an exemplary structure is known in which two prism sheets are arranged in a stack such that respective prism arrays of the two sheets are oriented orthogonally to each other, whereby light spreading in the two directions are efficiently condensed to improve front luminance (refer to Patent Document 1 below).
[Patent Document 1] PCT Japanese Translation Patent Publication No. 10-506500